1. Field of the Invention
The disclosed method relates generally to use of multi-state materials, such as chalcogenide, in semiconductor devices and, more particularly, relates to formation of a three-dimensional container diode that may be used in conjunction with a multi-state material memory element to form an electrical memory cell.
2. Description of Related Art
Multi-state materials are materials that can be caused to change physical states in response to an input stimulus. The use of programmable variable resistance materials, such as chalcogenide, amorphous silicon, or antifuse in electronic memories is known in the art. By way of example, chalcogenides are materials that may be electrically stimulated to change states and resistivities, from an amorphous state to a crystalline state, for example, or to exhibit different resistivities while in a crystalline state. A chalcogenide material may be predictably placed in a particular resistivity state by running a current of a certain amperage through it. The resistivity state so fixed will remain unchanged unless and until a current having a different amperage within the programming range is run through the chalcogenide material. Because of these unique characteristics, chalcogenide materials may be used in memory cells for storing data in binary or higher-based digital systems.
A chalcogenide-based memory cell typically includes a chalcogenide memory element for storing data and an access element, coupled to the memory element, for use in programming and sensing the stored data. The access element may be, in one embodiment, a diode. A chalcogenide-based memory cell will typically be accessible to external circuitry by the selective application of voltages to address lines, as are conventionally used in semiconductor memories.
Because of the unique operating characteristics of chalcogenide-based memories, control of current flow is crucial to facilitate programming. Programming of chalcogenide requires large current densities. In this regard, it is desirable that a chalcogenide-based memory cell include a diode large enough to permit a large current flow in the forward direction, while allowing essentially no current flow in the reverse direction. Conventional junction diode structures large enough to supply the necessary current require so much space on the upper surface of the silicon substrate that they negate the space-saving advantages of using chalcogenide in memories. Accordingly, there is a need for a small, easily manufactured diode that can meet the performance requirements of chalcogenide-based memory cells.